New York, USA – 23/09/2014 – as published by VICE News

At least 19 people were killed on the third day of a US-led air campaign targeting the Islamic State in Syria. Strikes focused on one of the group’s main revenue streams — the region’s captured oil fields.

Activists say that the attacks, made by the US along with five Arab allies, led to the release at least 150 people from a prison in their powerbase of Raqqa in northern Syria, as the militant group feared more strikes, according to the Associated Press.

At least 14 militants were killed in the attacks, which hit four oil installations and three oil fields near the town of Mayadeen in the east of the country. This information came from the UK-based Syrian Observatory for Human Rights (SOHR), which gathers reports from a network of activists on the ground, and was confirmed by two local activist groups.

SOHR also suggested that another five people killed in the strikes late on Wednesday night and early on Thursday morning near a refinery in the northeastern Hasakah province were the wives and children of Islamic State members.

Other strikes hit the group’s checkpoints, compounds, training grounds, and vehicles. Raids targeted Syrian military bases seized by the militants and hit a building used as an Islamic court, as well as a cultural center in Mayadeen, the activists reported.

Video capturing this second wave of strikes was posted to YouTube by an account titled “Coordinator Free Euphrates.” The footage shows flames and a large explosion believed to be the moment US airstrikes hit the city.

Strikes also took place in Syrian Kurdish areas. Fighters reported three airstrikes in Kobani, in the Aleppo region of northern Syria. Islamic State (formerly known as ISIS) militants have been attacking the city, also known as Ayn al-Arab, for nearly a week, causing thousands of Kurds to flee to neighboring Turkey.

A spokesman for the Kurdish fighters, Reydour Khalil, asked the coalition to coordinate with them, claiming that the overnight strikes were not effective and struck abandoned bases.

“We are willing to cooperate with the US and its alliance,” Khalil told the Associated Press, saying that they could provide information about the movements of Islamic State fighters.

The Islamic State is believed to control 11 oil fields in Iraq and Syria, earning between $2-3 million a day from oil smuggling, black market sales, theft, and extortion. Those funds have supported its rapid advance across much of Syria and Iraq, while reportedly expanding its army of jihadists from 10,000 to 50,000 in a couple of months.

Oil production and sales are crucial for the jihadist group as they attempt to evolve into a government and fully-fledged state. As one expert told Foreign Policy, ISIS has “gone from being the world’s richest terrorist organization to the world’s poorest state.”

An earlier wave of strikes targeted Islamic State positions in the northwest of al-Qa’im in Syria, two southeast of Irbil in Iraq, and two west of Baghdad, US Central Command said in a statement. At least 120 jihadists from the Islamic State and al Qaeda in Syria, as well as eight civilians, have been killed in the strikes so far, according to SOHR.

The US has been conducting air raids against the group in neighboring Iraq for more than a month but this week is the first time the Islamic State has been targeted in Syria. This has raised concerns about the impact strikes could have on the ongoing civil war there, although the Obama Administration were keen to dispel any suggestions they could be collaborating with the beleaguered, oppressive regime of Bashar al-Assad.